Google Calendar
Free
Google Calendar is a cloud based calendar from Google.
Org-mode
Open Source
Org-mode is an Emacs Mode for Notes, Planning, and Authoring.
Apple Calendar
Free
Calendar is a personal calendar application made by Apple Inc. that runs on both the macOS desktop operating system and iOS mobile operating system.
Compare Kontact - KOrganizer with alternatives
Compare Google Calendar and Kontact - KOrganizer and decide which is most suitable for you.
Compare Apple Calendar and Kontact - KOrganizer and decide which is most suitable for you.
Compare Org-mode and Kontact - KOrganizer and decide which is most suitable for you.